Some microorganisms such as Clostridium acetobutylicum or Clostridium beijerinckii are known to produce acetone or isopropanol as major by-products during butanol fermentation (ABE or IBE fermentation) [George H A, Johnson J L, Moore W E C, Holdeman L V, Chen J S: Acetone, isopropanol, and butanol production by Clostridium beijerinckii (syn. Clostridium butylicum) and Clostridium aurantibutyricum. Appl Environ Microbiol 45: 1160-1163]. However, all these organisms rely on sugar or starch based substrates. Acetogenic organisms such as the closely related microorganisms Clostridium autoethanogenum, C. ljungdahlii, and C. ragsdalei are able to grow chemoautotrophically on CO or CO2/H2 containing gases as sole energy and carbon source and synthesize products such as acetate, ethanol, or 2,3-butanediol, but neither acetone nor isopropanol [Munasinghe P C, Khanal S K: Biomass-derived syngas fermentation into biofuels: Opportunities and challenges. Bioresource Technol 2010, 5013-22].
Recently, production of isopropanol was reported in a study on Clostridium ragsdalei (Clostridium strain P11) in a 100-L pilot scale fermentor from switchgrass derived syngas [Kundiyana D K, Huhnke R L, Wilkins M R: Syngas fermentation in a 100-L pilot scale fermentor: Design and process considerations. J Biosci Bioeng 2010, 109: 492-498]. However, a related study from the same lab showed that this was due to a contamination in the used syngas since it was passed through a scrubbing mixture containing 20% acetone [Ramachandriya K D: Effect of biomass generated producer gas, methane and physical parameters on producer gas fermentations by Clostridium strain P11. Masters thesis, Oklahoma State University 2009]. The authors also noted that the production of isopropanol may be the result of reduction of propionic acid rather than acetone. Experiments carried out by the inventors of the present invention with Clostridium ragsdalei (Clostridium strain P11) and also C. autoethanogenum and C. ljungdahlii have never shown the production of acetone, isopropanol, or propionic acid.
The cost of many carbohydrate feed stocks suitable for the production of chemical products such as acetone and isoproanol is influenced by their value as human food or animal feed, and the cultivation of starch or sucrose-producing crops for such production is not economically sustainable in all geographies. Therefore, it is of interest to develop technologies to convert lower cost and/or more abundant carbon resources into useful chemical products such as acetone and isopropanol.
CO is a major free energy-rich by-product of the incomplete combustion of organic materials such as coal or oil and oil derived products. For example, the steel industry in Australia is reported to produce and release into the atmosphere over 500,000 tonnes of CO annually.
It is an object of the invention to overcome one or more of the disadvantages of the prior art, or to at least to provide the public with a useful choice.